Additives for lithium batteries and methods
Lithium tetrafluoro(malonato)phosphate compounds are useful as additives in lithium ion battery applications. The compounds are represented by Formula (I): MPF 4 [—O(C═O)—(CX′X″)—(C═O)O—]; wherein M is Li or Na; each X′ and X″ independently is selected from the group consisting of H, alkyl, fluoro-substituted alkyl, and F; or wherein the X′ and X″ together are —CR 2 —(CR′ 2 ) m —CR″ 2 —; each R, R′ and R″ independently is selected from the group consisting of H methyl, trifluoromethyl, and F; and in is 0 or 1. These compounds can be prepared in high purity and a high yield by reaction of a metal hexafluorophosphate with a bis-silyl malonate compound. A similar oxalato compound, lithium tetrafluoro(oxalato)phosphate), can be made in the same manner, but using a bis-silyl oxalate in place of the bis-silyl malonate. Advantageously, the compounds can be formed, in situ, in a LiPF 6 -containing electrolyte solution.
1. A method of preparing an electrolyte comprising MPF 6 and a salt of Formula (I) in a non-aqueous organic solvent; the method comprising adding a bis-silyl ester compound of Formula (II) to a solution of the MPF 6 in the non-aqueous organic solvent, and stirring the resulting mixture at ambient temperature for at least about 24 hours to form the salt of Formula (I), in situ;
wherein:
Formula (I) is MPF 4 [—O(C═O)—(CX′X″)—(C═O)O—];
Formula (II) is Z 3 Si—(C═O)—(CX′X″)—(C═O)O—SiZ 3 ;
M is Li or Na;
each X′ and X″ independently is selected from the group consisting of H, C 1 to C 4 alkyl, fluoro-substituted C 1 to C 4 alkyl, and F; or wherein the X′ and X″ together are an alkylene group of formula: —CR 2 —(CR′ 2 ) m —CR″ 2 —,
each R, R′ and R″ independently is selected from the group consisting of H, methyl, trifluoromethyl, and F, in is 0 or 1, and
each Z independently is C 1 to C 4 alkyl.
2. The method of claim 1 , wherein the non-aqueous organic solvent comprises at least one organic carbonate solvent.
3. The method of claim 1 , wherein at least one of X′ and X″ is F.
4. The method of claim 1 , wherein at least one of X′ and X″ is C 1 to C 4 alkyl.
5. The method of claim 1 , wherein X′ is F and X″ is methyl.
6. The method of claim 1 , wherein the compound of Formula (I) is formed in the electrolyte at a concentration in the range of about 0.5 to about 2 wt %.
7. The method of claim 1 , wherein the X′ and X″ together are an alkylene group of formula: —CR 2 —(CR′ 2 ) m —CR″ 2 —; and each R, R′ and R″ independently is selected from the group consisting of H and F.
8. The method of claim 1 , M is Li.
9. The method of claim 1 , wherein each Z is methyl.
10. The method of claim 1 , wherein byproduct FSiZ 3 that is formed by the reaction of the MPF 6 with the compound of Formula (II) is retained in the electrolyte.
11. The method of claim 1 , wherein byproduct FSiZ 3 that is formed by the reaction of the MPF 6 with the compound of Formula (II) is removed from the electrolyte by volatilizing the FSiZ 3 .
12. A method of preparing an electrolyte comprising MPF 6 and an additive comprising a compound of Formula (V) in a non-aqueous organic solvent:
the method comprising the steps of adding a bis-silyloxy compound of Formula (VI):
to a solution of the MPF h in the non-aqueous organic solvent, and stirring the resulting mixture at ambient temperature for at least about 24 hours to form the compound of Formula (V) in situ;
wherein:
M is Li or Na;
each Z independently is C 1 to C 4 alkyl; and
A is
wherein:
E is CH or N;
each Z′ independently is a substituent replacing a hydrogen atom and is selected from the group consisting of C 1 to C 4 alkylm halogen, alkoxy; and fluoro-substituted C 1 to C 4 alkyl;
x is 0, 1, 2, or 3 when E is N; and
x is 0, 1, 3, or 4, when E is CH.
13. The method of claim 12 , wherein each Z is methyl.
14. The method of claim 12 , wherein M is Li.
15. The method of claim 12 , wherein A is
wherein:
E is CH or N;
each Z′ independently is a substituent replacing a hydrogen atom and is selected from the group consisting of C 1 to C 4 alkyl, halogen, alkoxy; and fluoro-substituted C 1 C 4 alkyl;
x is 0, 1, 2, or 3 when E is N; and
x is 0, 1, 2, 3, or 4, when E is CH.
16. The method of claim 12 , wherein A is
wherein:
E is CH or N;
each Z′ independently is a substituent replacing a hydrogen atom and is selected from the group consisting of C 1 to C 4 alkyl, halogen, alkoxy; and fluoro-substituted C 1 to C 4 alkyl;
x is 0, 1, 2, or 3 when E is N; and
x is 0, 1, 2, 3, or 4, when E is CH.
17. The method of claim 12 , wherein A is
wherein:
E is CH or N;
each Z′ independently is a substituent replacing a hydrogen atom and is selected from the group consisting of C 1 to C 4 alkyl, halogen, alkoxy; and fluoro-substituted C 1 to C 4 alkyl;
x is 0, 1, 2, or 3 when E is N; and
x is 0, 1, 2, 3, or 4, when E is CH.
18. The method of claim 12 , wherein byproduct FSiZ 3 that is formed by the reaction of the MPF 6 with the compound of Formula (VI) is retained in the electrolyte.
19. The method of claim 12 , wherein byproduct FSiZ 3 that is formed by the reaction of the MPF 6 with the compound of Formula (VI) is removed from the electrolyte by volatilizing the FSiZ 3 .